The present invention relates to a duplex voice communication radio transmitter-receiver for transmission and reception of voice message with the use of radio waves having a single frequency or two adjacent frequencies.
It is known in common duplex operating radio communication that radio waves to be used should be of two sufficiently separated frequencies for stable and consistent transmission.
However, the duplex operation becomes possible with lower but acceptable effectiveness through the use of one frequency or two closely separated frequencies. FIG. 20 shows the schematic arrangement of "a narrow-band voice communication transmitter-receiver capable of simultaneously transmitting and receiving voice information with the use of radio waves of a single frequency".
As illustrated in FIG. 20, a couple of narrow-band voice transmitter-receiver B1 and B2 are identical in the construction employing one carrier frequency f for transmission and reception. Each transmitter-receiver contains a transmitter T, a receiver R, a control switch SW for selecting and activating either the transmitter or the receiver at intervals of a given time, a sync generator SYCGEN for controlling the intervals and synchronizing the control switch with a control switch of the other station, a loud-speaker SP, a microphone MIC, and an antenna coupler AT. Also, denoted by ANT is an antenna. (In FIG. 20, like components in the transmitter-receivers B1 and B2 are identified by the subscript numerals 1 and 2 respectively.)
The two transmitter-receivers are controlled with timing by their respective sync generators SYCGEN for transmission and reception in the alternate relationship with each other.
FIG. 21 illustrates a time chart showing the exchange of voice signals between the two narrow-band voice communication transmitter-receivers B1 and B2 portrayed in FIG. 20. Without regard to the subscript numerals, represented by VM is a transmitting voice signal, SWT is a shift pulse for transmission and reception generated by the control switch SW, and VSP is a received voice signal. Also, T is a transmission period of time, R is a reception period, and T0 is a cycle of transmission and reception. (Hence, the reciprocal of T0 or a repeat frequency is denoted by F0.)
In the operation between the two transmitter-receivers, the transmitting voice signal VM is sampled at intervals of time so that about a half of the same is received as the received voice signal VSP. This results in intermittent transmission of a signal from one station to the other. Fortunately, a voice sound of speech is redundant and the transmission of speaking sounds becomes possible if the repeat frequency F0 is appropriately predetermined. The received voice sounds are yet unfavorable to human ears and somewhat less audible.
For improvement, a method has been introduced in which the blank portions C0 of a signal resulting from time sampling are compensated. However, the result is still unsatisfactory and can hardly be appropriate for practical use.
Also, another type of duplex operating radio transmitter-receiver has been developed in which the transmitter delivers intermittent radio signals on a modulated carrier through time dividing an original voice signal and compressing a talk duration and the receiver, upon receiving and detecting the transmitting radio signals, demodulates them to the original voice signal by time expanding and rebinding the intermittent signals in synchronism with the action of the transmitter. The synchronizing action is controlled by one of the two transmitter-receivers which serves as a "master station" and is arranged to determine the time allocation of time divided segments of a modulated signal during transmission so that the other transmitter-receiver which serves as a "slave station" can be actuated in synchronism.
This transmitter-receiver will now be explained in more detail referring to the drawings.
FIG. 10 shows an arrangement of the transmitter-receiver, as compared to the arrangement shown in FIG. 20. The narrow-band voice communication transmitter-receivers B1 and B2 are identical in block diagram representation to those illustrated in FIG. 20, although the subscript numerals in FIG. 10 are of large size for distinction from those of small size in FIG. 20. FIG. 11 is a time chart, similar to FIG. 21, showing the exchange of voice signals between the two transmitter-receivers B1 and B2. Without regard to the numeral subscripts, represented by VM is a transmitting voice signal, SWT is a shift pulse for transmission and reception generated by a control switch SW, and VSP is a received voice signal. The shift in SWT is carried out in every half of T0 during intermittent transmission of the voice signal.
A voice signal transmitted from the transmitter-receiver B1 to B2 is denoted by the real line while another voice signal from B2 to B1 is denoted by the dotted line. A difference of the exchange of those signals shown in FIG. 11 from in FIG. 21 is that the voice signal is processed by time compression and expansion. More specifically, at the transmission side, a transmitting voice signal VM derived from a microphone MIC, which is represented by the numeral 1 (or 5)--the numeral in brackets will represent a signal expressed by the phantom lines hereinafter--is time divided at equal intervals and time compressed to 1/2 as represented by 2 (or 6) and thus, becomes a series of carrier modulated signals of time compressed voice information which are in turn transmitted as an intermittent radio wave. At the reception side, the time compressed, intermittent voice signals 7 (or 3) after received and detected are time expanded and bound together in sequence to a continuous voice signal 8 (or 4) which is converted to acoustic energy by a loudspeaker SP for sound reproduction.
As the result of the above process, continuous quality voice sounds unlike the unfavorable intermittent sounds shown in FIG. 21 will be delivered to listener's ears. The radio wave employed has only one frequency f and still enables "duplex operating communications" which is commonly executed with conventional wire telephones.
The processing of voice sounds including "time division", "time compression", and "time expansion" can be implemented by an analog or digital procedure.
Both the analog and digital procedure are illustrated in detail in FIGS. 12, 13, and 14.
FIG. 13 is a block diagram showing a transmitter for execution of the analog procedure (in which the subscript numeral 1 is not shown for simplicity).
A clock frequency 2 fCLK delivered from a reference oscillator OSC is divided by a 1/2 divider DIV to a clock frequency fCLK which is in turn fed to a switch controller SWCONT. Those components constitute in combination the sync generator SYCGEN shown in FIG. 10.
The switch controller SWCONT is arranged for control of a control switch SW comprising three co-operable switches SWa, SWb, and SWc.
FIG. 12 is a timing chart showing the action of FIG. 13.
The action will now be described referring to FIGS. 12 and 13. A voice signal VM is suppressed by an anti-aliasing noise removing lowpass filter AALPF (which is adapted for not limiting the band of voice frequencies but preventing the mixture of a sampling noise with the voice signal) to a frequency band of not more than 3 kHz so as to avoid interference with the clock frequencies fCLK and 2 fCLK and then, written into a couple of analog shift registers ASRa and ASRb alternately. Subsequently, the band suppressed voice signal is read from the two analog shift registers ASRa and ASRb. Both writing and reading speeds are proportional to clock frequencies supplied to their respective analog shift registers. First, the clock frequency fCLK is fed via the switch SWc to ASRa into which the voice signal is recorded during a storage time Ts. Upon completion of the writing, all the switches are turned over. (FIG. 13 shows a state just after the turning over of the switches.)
The clock frequency for ASRa is then changed to 2 fCLK by the switchover action of the switch SWc. Simultaneously, the voice signal which has been time compressed is transferred at a speed of two times the writing speed (i.e. during an output time Tc which equals 1/2 of the storage time Ts) via the switch SWa to a band-limit filter BLLPF. This action is denoted in the first row of the chart of FIG. 12.
During the output time Tc, the voice signal is written into the analog shift register ASRb throughout the storage time Ts using the clock frequency fCLK supplied through the switch SWb. After completion of the writing, the switch SWb is turned over and the clock frequency is shifted to 2 fCLK. Accordingly, the time compressed voice signal is fed via the switch SWa to the band-limit filter BLLPF at a speed of two times the writing speed (i.e. during the output time Tc which equals 1/2 of the storage time Ts). This action is denoted in the second row of the chart of FIG. 12.
At the moment when the signal output from ASRa has been completed as shown in the first row, the writing into ASRb shown in the second row is halfway through. Thus, the output of the band-limit filter BLLPF is followed by a blank period which equals Ts-Tc or 1/2 of Ts.
As the actions shown in the first and second rows are repeated alternately, a series of intermittent voice signals shown in the third row of the chart of FIG. 12 are output from the band-limit filter BLLPF. Those intermittent voice signals are equal to the intermittent signals represented by 2 (or 6) of FIG. 11. The description of "time division" and "time compression" in the analog procedure of a voice signal at the transmission side is now finished.
The "time expansion" and demodulation in the analog procedure of a voice signal at the reception side is executed by the arrangement similar to that of FIG. 13, in which like components are denoted by like abbreviations accompanied with the subscript numeral 2 while both AALPF and BLLPF are not used. In operation, VM is an intermittent, compressed voice signal acquired through reception and detection while the clock frequencies fCLK and 2 fCLK are supplied in reverse by the action of the control switch SW.
Accordingly, a resultant continuous, time compressed voice signal given through demodulation is reproduced, at the absence of the band-limit filter BLLPF, in the form denoted by 8 (or 4) of FIG. 11.
FIG. 16 is a block diagram showing in more detail the arrangement of the transmitter-receiver B1 shown in FIG. 18 (which is equal to that of B2 at the other station).
A reference oscillator OSC1 is adapted to trigger a flip-flop FF1 using a frequency of a few hertz. The flip-flop FF1 activates a transmitter TX1 and a receiver RX1 alternately for on/off operation. The terminal Q1 of the flip-flop FF1 delivers command signals for actuating the transmitter TX1 and performing the 1/2 time compression of the voice signal and the terminal Q1 for actuating the receiver RX1 and the x2 time expansion of the voice signal.
In operation, the voice signal from a microphone MIC1 is time divided and compressed by an audio processor VSD1 to an intermittent signal such as denoted by 2 of FIG. 11 (also, shown in the third row of FIG. 12). The intermittent signal is then modulated by the transmitter TX1 and transferred via an antenna coupler AT1 to an antenna ANT1 from which it is emitted in the form of a radio wave.
The receiver RX1 is then triggered by a command signal from the terminal Q1 for receiving the intermittent radio wave transmitted from the transceiver B2 of the slave station.
The intermittent radio wave after received is delivered to a front end high-frequency amplifier RXFE1 (which contains a mixer and is coupled to the input of an intermediate-frequency amplifier IFA1) and fed across the intermediate-frequency amplifier IFA1 to a detector DET1 where it is detected and further, transferred to a signal processor VSH1. The signal processor VSH1 repeats two alternate actions which are opposite to the actions expressed in the first and second rows of FIG. 12, in which each unit segment of the intermittent signal is fed during the high level at Q1 and time expanded until the next high level is induced. A resultant continuous voice signal is then fed via an audio power amplifier PA1 to a loudspeaker SP1 for sound reproduction. As also shown in FIG. 16, the aforementioned repeating operation of the two alternate actions is accurately controlled by both a square-wave signal TSG1 which is supplied from the terminal Q1 along a line TL1 to a front end TXFE1 disposed in front of a modulator MOD1 in the transmitter TX1 and a square-wave signal RSG1 which is supplied from the terminal Q1 along a line RL1 to the receiver RX1.
It should be understood that both the square-wave signals TSG1 and RSG1 of the transmitter-receiver B1 have to be correctly synchronized with those, TSG2 and RSG2, of B2 for synchronous communication between B1 and B2.
FIG. 17 is a block diagram showing a transmitter-receiver which acts as a slave station receiver and is arranged to actuate in synchronism with the action of the master station transmitter of FIG. 16. FIG. 18 shows a block diagram of the primary parts of their respective transmitter-receivers shown in FIGS. 16 and 17 for ease of description of the synchronizing action. FIG. 19 is a timing chart illustrating the synchronizing action between the two stations.
In the synchronizing action, the master station needs no particular procedure while the slave station is controlled corresponding to the action of the master station. More specifically, the slave station is actuated for the synchronization in which a carrier signal is picked up from the input of a detector DET2 by a carrier detector CAD2 and then, the decay CU2 of a resultant carrier detection signal 5 shown in FIG. 19 is detected by a decay detector CAP2 to develop TP2 of a pulse signal 6 which is in turn fed as a trigger signal to a monostable multivibrator MB2 provided in place of the flip-flop FF1 of FIG. 16. The multivibrator MB2 then delivers from its terminals Q2 and Q2 two square-wave signals TSG2 and RSG2 respectively for control of voice signal processing and thus, the synchronizing action will be ensured.
In more detail, the slave station B2 when energized or serving as the receiver remains in a reception standby state with the monostable multivibrator MB2 closed at Q2 and upon reception of a transmitting signal from the master station B2, allows a detection signal 5 to be generated from a received carrier signal 4 of the intermediate-frequency amplifier IFA2, as shown in FIG. 19. The decay of the detection signal 5 is then detected by the detector CAP2 (a differentiating circuit) for generating a trigger pulse TP2. The trigger pulse TP2, which is a signal of completion of the signal transmission and start of the signal reception at the master station, causes the monostable multivibrator MB2 to switch over the operation and deliver the square-wave signal TSG2 8 for transmission while the square-wave signal RSG2 7 for reception is halted. The duration of the switch action of the monostable multivibrator MB2 is determined by the timing of the master station B1 so that B2 can automatically be turned back to the reception state when B1 shifts from the reception state to the transmission state.
The synchronizing action described above is an example and various other synchronizing methods will equally be employed.
Also, the monostable multivibrator MB2 in the slave station may be replaced with a flip-flop circuit which will be activated by a trigger pulse associated with both the rise and decay in the detection signal 5 derived from a received carrier signal 4 of the intermediate-frequency amplifier IFA2. In this case, the rate of time compression other than the repeat time T0 can be detected in the slave station and used for determining a ratio between transmission and reception periods of the slave station, whereby the synchronizing procedure will be facilitated.
Furthermore, the synchronizing action may be executed by an independent synchronization method in which reference signals emitted from two reference oscillators provided in their respective communicating transmitter-receivers B1 and B2 are utilized for generating timing signals for transmission and reception which are then processed in correlation relationship for synchronization between B1 and B2. This method however claims a considerable length of time before the synchronizing action is completed and also, will be more disadvantageous in the respect of cost than the previous method. The advantages of this method are that the two stations are less discriminated from each other thus increasing the freedom of communications and that error in the synchronizing action is minimized whereby communication stability will be enhanced.
It would be understood that the transmitter-receiver also acts as a common press-talk type transceiver when an additional component for temporarily canceling the action of both the audio processor and the synchronizing device is installed.
FIG. 14 is a block diagram for use in the digital processing of voice signals.
In operation at the transmission side, a transmitting voice signal VM is filtered by AALPF for band suppression, converted into a digital form by an A/D converter ADC, and transferred at a common speed (e.g. 8 kHz) to a random access memory RAM for storage at a given address. After a predetermined period of this action, the signal is read out at a speed of two times the common speed (hence, 16 kHz) and converted back to an analog form by a D/A converter DAC in the same manner as expressed in the first row of the chart of FIG. 12.
Just after the completion of storage of the preceding signal, a succeeding signal is stored into another address of the RAM and retrieved subsequently, which is illustrated in the second row of FIG. 12.
Then, the repeating of both the first and second row procedures results in generation of an intermittent signal, as shown in the third row of FIG. 12, which is in turn output through a band-limit filter BLLPF.
Also, the foregoing procedures are controlled by an audio signal pitch controller CTR containing a microcomputer. In other words, this CTR serves as a combination of SYCGEN and SW of FIG. 10 (cf. like controllers shown in FIGS. 16 to 18 will operate the same as described later). More particularly, CTR delivers start signals to the converters ADC and DAC respectively and controls the memory RAM for determining a storage location and performing the writing and reading at different speeds.
In operation at the reception side, the intermittent, compressed voice signal acquired through reception and detection is processed for demodulation by the arrangement shown in the block diagram of FIG. 14 at reverse writing and reading speeds and in a reverse manner and then, delivered as a common continuous voice signal.
Those conventional duplex voice communication transmitter-receivers however have some disadvantages.
Such disadvantages are particularly emphasized in the articulation and intelligibility of voice sounds. Among them is that when the frequency range (occupied band width) of an assigned radio wave for use in communication is legally defined by two limited values, the compression of a voice signal may result in increase of the range and surpass of the limited value thus causing radio interference.
Another disadvantage resides in synchronous error.
When a synchronous error is caused during expansion and rebinding of divided components of a received signal in the reception side and a resultant reproduced signal contains gaps, unwanted noises such as burst sounds will appear rendering the reproduced voice message inaudible. Accordingly, the synchronizing action should always be executed by such a definite and tough manner as never being affected by fading.
Also, a further disadvantage is that a specific measure is needed for allowing the master station (which transmits voice information) to select a target slave station (which receives the information) from a number of local stations because the communication is carried out using one signal frequency between two different stations which are designated as a master station and a slave station. If the selection of one single slave station fails, the communication of the master station will be involved with plural slave stations concurrently thus causing confusion.
A still further disadvantage resides in time delay which will be induced during the voice processing including "time division", "time compression", and "time expansion" and "signal rebinding". The time delay will slow down the velocity of communications as if they are exchanged through a satellite circuit.
It is thus an object of the present invention to provide a duplex voice communication radio transmitter-receiver which is capable of operating even when the frequency range of a legally assigned radio wave used for communication is strictly limited, much improved in the use of a frequency, less affected by fading, enhanced in the ability of secret communication, and arranged to provide no slowdown during the communication and higher articulation and intelligibility in reproduced sound.